Amorphous polyolefins (APOs) are well known and are very useful in adhesives, roofing compositions, cable flooding, caulks and sealants. APOs are produced and transferred or shipped in many forms for incorporation into final compositions. APOs are generally tacky at room temperature and have a low degree of crystallinity and are therefore, not easily formed into powders or pellets for shipment.
The manufacturers of APOs, and other thermoplastic materials having similar melt viscosities, have struggled with finding an economical and practical way of delivering these raw materials to compounders or end users in a form that is generally easily manageable and cost efficient. There have been serious shortcomings in finding practical transportation means and user-friendly packaging for APOs. Many compounders and end users are not equipped to handle tank cars of bulk molten material. Small solid APO slats coated with a non-tacky substance are more useable, but are much more expensive due to high production processing costs. The form most economical to use is solid APO blocks packaged in release coated paper. However, the unwrapping and handling of a solid APO block is very labor intensive and generates substantial paper waste.
There have been several processes aimed at providing useful solid forms of low viscosity hot-melt, thermoplastic products such as hot-melt adhesives, APOs and asphalt compositions that do not require unwrapping. U.S. Pat. No. 4,748,796 (1988) discloses an elaborate process of solidifying adhesive compositions in molds which are coated with an electrostatically held screen of powder. U.S. Pat. No. 5,160,686 (1992) discloses another process involving complicated machinery for blowing a hot gas curtain between a polypropylene mold and a stream of hot-melt-blown hydrogenated castor oil designed to coat a molten hot melt adhesive as it solidifies.
U.S. Pat. No. 5,109,892 (1992) discloses a process wherein a rigid free-standing thick walled (0.25-4 mm) polyolefin container is filled with molten APO without melting, even though the container has a melting point below the temperature at which the molten APO is flowed into the container. U.S. Pat. No. 5,109,892 discloses that the relationship between the maximum fill temperature and the container thickness for that process is demonstrated by the linear equation wherein the fill temperature is preferably less than about Y.degree. C., wherein Y equals 0.34 times the melting point of the container material (.degree. C.), times the minimum wall thickness of the container (mm), plus 143. For packaging of APOs in polyolefin containers at flowable fill temperatures, this equation limits container thickness to no less than about 0.25 mm.
The process of U.S. Pat. No. 5,109,892 is attractive since there are no wasteful molds or elaborate cooling methods required. However, the polyolefin container has provided too great of a percentage of polyolefin when the APO or other similar viscosity thermoplastic material and container are melted together for end use. Also, thicker walled molded containers are relatively more expensive to make than thin walled molded containers.
Since then, alternate processes using thin walled containers have been disclosed and require very elaborate and expensive equipment. U.S. Pat. No. 5,292,468 (1994) discloses a process involving spinning nozzles which spray a complex protective web of non-pressure sensitive adhesive into the interior of a mold prior to filling with hot melt adhesive.
U.S. Pat. No. 5,307,608 (1994) discloses a process for packaging asphalt wherein a floatable mold is lined with a 0.025 to 0.45 mm polypropylene or polyethylene film required to have a melting point higher than the molten fill temperature. The small percentage of container material in the solid package is very useful. But the disclosed process requires an elaborate conveyor driven cooling system to keep the container material from melting.
U.S. Pat. No. 5,401,455 (1995) discloses another process using a thin (0.0025-0.125 mm) polyethylene based nonrigid film requiring a mold and either a heat sink or refrigerant to keep the thin film from melting.
In light of the above, it would be very desirable to be able to cheaply produce APOs or materials having similar melt viscosities in a solid non-tacky form having a small percentage of packaging which can be melted along with the material being packaged. It would further be desirable to have a process utilizing a thin walled container requiring no waste while requiring no heat sinks or elaborate cooling equipment.